/**
 * Simple wrapper for the native GraphicBuffer class.
 * @hide
 */
public class GraphicBuffer implements Parcelable {
    ...
    private final int mWidth;
    private final int mHeight;
    private final int mFormat;
    private final int mUsage;
    // Note: do not rename, this field is used by native code
    private final long mNativeObject;

    // These two fields are only used by lock/unlockCanvas()
    private Canvas mCanvas;
    private int mSaveCount;
    ...
}

• GraphicBuffer 的宽高、像素格式、usage 等成员描述 buffer 属性。
• mNativeObject 是 GraphicBufferWrapper 地址。
• 在 lockCanvas() 创建 mCanvas。